Cathodic protection evaluation: final report

This research investigates the effectiveness of a new corrosion rate test instrument in making field evaluations of the corrosion condition of several conventionally reinforced concrete coastal bridges. The instrument is the Gecor 9 Corrosion Rate Meter and comes with several sensors. This device is able to perform several techniques to evaluate the corrosion activity of steel reinforcement under diverse conditions. The Gecor's Sensor A is equipped with three reference electrodes (RE), 1 counter electrode (CE), and 1 guard electrode (GE). Sensor A was used to measure the rebar corrosion current, i [subscript corr], using a DC galvanostatic pulse with modulated applied current confinement. This procedure was used to obtain baseline data for 21 zones of an impressed current cathodic protection (ICCP) system recently installed on the Conde McCullough Bridge in Coos Bay. That same procedure was also used to evaluate the reinforcement corrosion activity at two failed ICCP zones at the Yaquina Bay Bridge. Both of those ICCP systems utilized thermally sprayed zinc as distributed anodes. Sensor A is also able to perform an AC-based test to qualitatively evaluate the effectiveness of cathodic protection (CP) systems without the need to interrupt the applied CP current. That test protocol was applied to the same 21 ICCP zones at the Coos Bay Bridge and to six test location of the Lint Creek Bridge that has a galvanic anode CP (GACP) system installed to control rebar corrosion. Gecor Sensor B is equipped with one RE and one CE and is used to concurrently measure a rebar's corrosion potential, E [subscript corr], and the resistivity of the surrounding concrete. Firmware in the Gecor 9 uses the observed corrosion potential and concrete resistivity to state the corrosion risk for the steel at the location tested. In general, the Gecor 9 performed very well. However, although it is a sophisticated instrument, it is able to produce data that is clearly questionable. Fortunately, since the Gecor has the ability to perform several markedly different types of tests, inconsistencies are generally obvious and a suspicious reading can be re-tested. Measurement errors were less a problem on the Yaquina Bay and Lint Creek Bridges because rebar could be clearly located before testing. At Coos Bay, the presence of a new zinc coating interfered with being able to identify rebar locations prior to removing the zinc on the concrete surface. At locations where reference electrodes were present and in areas of rebar structure bonds, a reasonable estimation of the rebar location could be made prior to removal of the zinc anode over an area of 8-9 inches in diameter to allow testing with the Gecor. Generally speaking, the Gecor 9 was able to make reasonable evaluations of cathodically protected rebar without having to interrupt the CP system. In terms of CP operation, this research demonstrated that: 1) the GACP system at Lint Creek is working well and protecting the embedded rebar; 2) All 12 locations tested in the two failed CP zones at Yaquina Bay reflect passive behavior of the embedded rebar even after the CP current had been interrupted for a number of years; Although the Gecor performance at Coos Bay was not as consistent as observed at the other bridges, it appears for future application, if rebars at test locations were located prior to applying the zinc coating, the test could be conducted with the sensor in proper alignment with the embedded steel, and that would significantly improve the performance of the instrument.Report -- Appendices.This archived document is maintained by the Oregon State Library as part of the Oregon Documents Depository Program. It is for informational purposes and may not be suitable for legal purposes.Title from PDF title page (viewed on April 6, 2015)."ODOT Contract PSK28885."Includes bibliographical references (pages 66-69).Sponsored by Oregon Department of Transportation, Bridge Preservation Unit PSK28885Mode of access: Internet from the Oregon Government Publications Collection.Text in English.Draft final report